Testing for Ions

Types of tests and what colours and precipitates they form

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Testing for positive Ions

 Flame tests

Sodium (Na+) - Yellow, Potassium (k+) - Lilac, Calcium (Ca2+) - Brick red

Copper (Cu2+) - Blue/green

Sodium Hydroxide tests

Calcium (Ca2+) - White - Ca(OH)2

Copper(II) (Cu2+) - Blue - Cu(OH)2

Iron(II) (Fe2+) - Sludgy Green - Fe(OH)2

Iron(III) (Fe3+) - Reddish brown - Fe(OH)3

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Tests for Negative Ions

 Carbonate ions give off CO2 (and water), Sulphites give of SO2 (and water) tested using potassium dichromate paper (orange to green).

Sulphate ions produce a white precipitate with  dilute HCl and Barium Chloride (HCl removes and carbonates of sulphites before the test).

Nitric acid and silver nitrate: tests for halides

Chloride ions give a white precipitate - Silver Chloride

Bromide ions give a cream precipitate - Silver Bromide

Iodide ions give a yellow precipitate - Silver Iodide

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